Haskell `mkDerivation` Configuration and Dependency Specification

to lift any version constraints in the cabal file. Note that this can't lift version bounds if they are conditional, i.e. if a dependency is hidden behind a flag. `enableParallelBuilding` : Whether to use the `-j` flag to make GHC/Cabal start multiple jobs in parallel. `maxBuildCores` : Upper limit of jobs to use in parallel for compilation regardless of `$NIX_BUILD_CORES`. Defaults to 16 as Haskell compilation with GHC currently sees a [performance regression](https://gitlab.haskell.org/ghc/ghc/-/issues/9221) if too many parallel jobs are used. `doCoverage` : Whether to generate and install files needed for [HPC][haskell-program-coverage]. Defaults to `false`. `doHaddock` : Whether to build (HTML) documentation using [haddock][haddock]. Defaults to `true` if supported. `testTargets` : Names of the test suites to build and run. If unset, all test suites will be executed. `preCompileBuildDriver` : Shell code to run before compiling `Setup.hs`. `postCompileBuildDriver` : Shell code to run after compiling `Setup.hs`. `preHaddock` : Shell code to run before building documentation using haddock. `postHaddock` : Shell code to run after building documentation using haddock. `coreSetup` : Whether to only allow core libraries to be used while building `Setup.hs`. Defaults to `false`. `useCpphs` : Whether to enable the [cpphs][cpphs] preprocessor. Defaults to `false`. `enableSeparateBinOutput` : Whether to install executables to a separate `bin` output. Defaults to `false`. `enableSeparateDataOutput` : Whether to install data files shipped with the package to a separate `data` output. Defaults to `false`. `enableSeparateDocOutput` : Whether to install documentation to a separate `doc` output. Is automatically enabled if `doHaddock` is `true`. `enableSeparateIntermediatesOutput` : When `doInstallIntermediates` is true, whether to install intermediate build products to a separate `intermediates` output. See [“Incremental builds”](#haskell-incremental-builds) for more information. Defaults to `false`. `allowInconsistentDependencies` : If enabled, allow multiple versions of the same Haskell package in the dependency tree at configure time. Often in such a situation compilation would later fail because of type mismatches. Defaults to `false`. `enableLibraryForGhci` : Build and install a special object file for GHCi. This improves performance when loading the library in the REPL, but requires extra build time and disk space. Defaults to `false`. `previousIntermediates` : If non-null, intermediate build artifacts are copied from this input to `dist/build` before performing compiling. See [“Incremental builds”](#haskell-incremental-builds) for more information. Defaults to `null`. `buildTarget` : Name of the executable or library to build and install. If unset, all available targets are built and installed. ### Specifying dependencies {#haskell-derivation-deps} Since `haskellPackages.mkDerivation` is intended to be generated from cabal files, it reflects cabal's way of specifying dependencies. For one, dependencies are grouped by what part of the package they belong to. This helps to reduce the dependency closure of a derivation, for example benchmark dependencies are not included if `doBenchmark == false`. `setup*Depends` : dependencies necessary to compile `Setup.hs` `library*Depends` : dependencies of a library contained in the package `executable*Depends` : dependencies of an executable contained in the package `test*Depends` : dependencies of a test suite contained in the package `benchmark*Depends` : dependencies of a benchmark contained in the package The other categorization relates to the way the package depends on the dependency: `*ToolDepends` : Tools we need to run as part of the build process. They are added to the derivation's `nativeBuildInputs`. `*HaskellDepends` : Haskell libraries the package depends on. They are added to `propagatedBuildInputs`. `*SystemDepends` : Non-Haskell libraries the package depends on.

This chunk details additional configuration arguments for `haskellPackages.mkDerivation`, covering parallel building (`enableParallelBuilding`, `maxBuildCores`), code coverage (`doCoverage`), Haddock documentation (`doHaddock`), and custom build hooks (`preHaddock`, `postHaddock`, etc.). It includes options for restricting `Setup.hs` to core libraries (`coreSetup`), enabling `cpphs`, and various `enableSeparate*Output` flags for separating build artifacts (executables, data, documentation, intermediates). Further options allow inconsistent dependencies, GHCi-specific library builds, and incremental build inputs (`previousIntermediates`). The text then introduces dependency specification, explaining how `mkDerivation` groups dependencies by package component (e.g., `setup*Depends`, `library*Depends`) and by type (e.g., `*ToolDepends` for build tools, `*HaskellDepends` for Haskell libraries, `*SystemDepends` for non-Haskell libraries).